Biological microarrays have proven to be valuable tools, enabling the addressable, parallel analysis of thousands of different analytes. However, there is still room for improvement of the substrates upon which such microarrays have been developed. A microarray substrate desirably has the following characteristics: 1) its surface chemistry should be stable for multiple uses and provide reliable quantitative analysis; 2) it should give low autofluorescence and achieve a high signal-to-background ratio to allow the detection of low analyte concentrations, such as those encountered in gene expression analysis; and 3) it should enable localization of appropriate target molecules. Currently, most commercial microarray substrates are composed of monolayers of aldehyde, amine, or epoxide-functional molecules directly anchored to substrates such as glass, silicon or gold. Unfortunately, these monolayers present substrate-specific bonding characteristics and provide a limited density of functional groups.
Polymer films are an alternative to molecular monolayers for use as microarray substrates. However, such films typically suffer from poor stability in most mediums, leading to degradation and/or delamination of the film from the substrate. One approach to preventing delamination is to employ reactive polymer coatings wherein the polymer has functional groups that can covalently bind to specific groups on an underlying substrate. Unfortunately, this approach to stable functionalization requires modification of both the polymer and the substrate and is generally effective with only a few substrates, such as glass and silicon.
Epoxy-functional polymers are potential candidates for polymer coatings in microarrays. Epoxide-containing polymers have been previously used in various applications, including the production of films for anchoring small molecules and forming imaging layers. However, most of these polymers are uncrosslinked films with poor stability and a tendency to delaminate. In addition, the few reports that exist on the use of crosslinked films do not disclose decoupling the crosslinking chemistry from the binding chemistry and, therefore, are characterized by relatively low densities of functional groups available for binding after crosslinking has occurred.